Piezoelectric crystal



May 9, 1939- J. M. woLFsKlLL 2,157,808

PIEZOELECTRIC CRYSTAL Filed Aug. 27, 1955 `faxla YaX/s 1 (eleg-ic] gPatented May 9,1939 2,157,8@8

UNITED STATES earl-:Nr ortica PIEZGELECTRIC CRYSTAL' John M. Wolfskiil,Erie, Pa., assignor to Bliley Electric Company, Erie, Pa., a partnershipcomposed of F. Dawson Bliley and Charles Cullman Application August 27,1935, Serial No. SiLlEd 3 Claims. (Cl. Til- 327) This invention relatesto piezo-electric crystals ultra-high frequency oscillations which it isdeand apparatus for employing piezo-electric cryssired to produce and/orstabilize. tais, generally. More particularly this invention Myinvention greatly simplifies piezo-electric relates to piezo-electriccrystals and apparatus quartz crystal controlled oscillation generation5 for employing piezo-electric crystals adapted for inasmuch as iteliminates the necessity of em- 5 generating ultra-high frequencyelectric oscilploying frequency doublers and frequency multilemonspliers. This is a material advantage since losses An object oi thisinvention is to provide a in frequency doublers and multipliers areenorpiezo-electrlc crystal adapted for harmonic opmous when Working withoscillations having 3o eration. frequencies higher than 30.0 megacycles.My inw Another object of this invention is to provide vention readilyproduces oscillations higher than a piezo-electric crystal adapted tooscillate e- 30.6 megacycles which are frequency stabilized, ciently atfrequencies which/are materially highwithout requiring the use of anyfrequency douer than its fundamental frequency. blers and multipliers.

A further object of this invention is to pro- I accomplish this bycutting or grinding the l5 vide a piezo-electric crystal adapted tosustain crystal in such a manner that its vibrations on oscillationswhich bear an harmonic relation to the harmonic frequencies arestronger. l prefer its fundamental frequency. to employ a transverse orshear vibration, and in Still a further object of this invention is toso doing greatly increase the strength of the viprovide a piezo-electriccrystal of quartz ground brations corresponding to the odd harmonics. 20to a thickness such that the fundamental fre- Vibrations other than thetransverse or shear quency of the crystal is in the neighborhood of typemay be employed.

i megacycles and operating the crystal on a By harmonics or harmonicfrequencies mean harmonic of the fundamental frequency fOr Sbavariousfrequencies called overtones which are bilizing the frequency ofelectric oscillations o approximately integral multiples of the iunda-25 said harmonic frequency. mental frequency. Thus, odd harmonics wouldStill another object of this invention is to probe approximately midmultiples, of the funda- Vide Piezo-electric Crystal OSCillatOr adaptedmental frequency. .By selecting odd harmonics to stabilize thefrequencies of oscillations of such as the third, nfth, seventh, ninth,eleventh,

39 ultra-high frequencies. and so on, of `for example, a crystal thatwill 30 Still another object of this invention is to prooscillare on afundamental frequency of 7,5 megvide a DeZO-el'bl Cri/Stal Cut andgIOUIld in acycles, vibrations of ultra-high frequencies such such amanner that the crystal can be made to as 22.5 megacycles correspondingto the third oscillate at frequencies which hear an harmonic harmonic,37,5 megacycles Correspnnding to the relation to the fundamentalthickness vibration ifm harmonic, 52.5 megacycles corresponding to 35frequency. the seventh harmonic, 67.5 megacycles corre- Still anotherobject of this invention is to pro- Sponding to the ninth harmonic maybe Obtained vide a crystal oscillation generator adapted to directlyfrom the crystal oscillator. The crysoscillate readily and emciently atany one ci a tal will he 3, 5, 7, or 9 times, etc., thicker than oseries of progressively increasing high irequenif it were operating onits fundamental at the w cies, same frequency.

Other and further objects of this invention 1D this manner the crystalvibrating on an will be apparent from the following specification113121110310 @an De used as the pllmaly Source oi and claims.oscillations when employed in a vacuum tube In accordance with thisinvention l provide CFCF'. and fm1 not necessarily be Simply a 45 meansemploying an element exhibiting piezo stabilizing device in a selfoscillatory circuit. electric properties for generating and/orstabilizcrrgh; 'lerugegnnythb g2? eiuclglgsn cehpezn; erated on itsharmonics when used as a resonator roducin some reaction on an associatenetthat it readily produces and stabilizes high frevjvork, or git may beused in filter circujts fluency oscillations 0f extremely high frequen'A further advantage of this invention is that cies. This iSaCCOmI-Jlished by Selecting a Crystal, piezo-electric plates or elementsmay be ground the fundamental frequency 0f which bears an to a thicknesssufcient to withstand normal use .55 harmonic relationship to thefrequency of the without breakage. Electrical oscillations as high asthose produced by piezo-electric elements of myv invention could not beproduced with piezo-electric elements of conventional cuts because thepiezo-electric elements would have to be ground too thin and fragile,and would be impractical even if the quartz could be ground to therequired dimension.

Other features and advantages of this invention will be apparent fromthe following specification and the accompanying drawing in which,brieiiy, Figure 1 illustrates the manner in which the crystal of myinvention is cut from the quartz hexahedron; Figure 2 illustrates theorientation of a crystal with respect to the various crystallographicaxes; Figure 3 illustrates an embodiment of a circuit arrangement inwhich the crystal of my invention may vibrate to produce oscillationsand Fig. 4 illustrates enlarged views of the shear mode of vibration ina crystal element.

Referring to Fig. 1 of the drawing in detail, reference numeral Idesignates a section of a quartz hexahedron from which a plate or slab2,

adapted to be used as a piezo-electric crystal, is

cut. The position of the plate 2 in the quartz hexahedronal crystal isshown in Fig. 1a, with respect to the :c or electric axis and the y ormechanical axis. Fig 1b shows the angle at which the crystal plate iscut with respect to the z or optic axis. In Fig. la the quartzhexahedron is shown with the optic or 2 axis at right angles to the :I:and y axes which are illustrated in the same plane. Fig. 1b, however,shows the y and z axes in the same plane and the a axis at right anglesto that plane. The plate 2 is cut from the crystal I in the mannershown, with the principal surfaces 3 and 4 of the plate, cut at an angleil with respect to the optic or z axis. The principal surfaces 3 and 4are cut substantially parallel to the electric or a: axis.

'Ihe values of the angle e may vary over rather wide limits, however,for best operation on harmonic frequencies, I have found that the plateshould be cut at angles of plus 30 degrees or minus 19 degrees. Forexample, a crystal which would oscillate at 15 megacycles would beapproximately .013" thick for the 30 out and approximately .018" thickfor the 19 cut. These thicknesses give strong, practical crystal platessatisfactory for use in electrical circuits.

The minus 19 degree angle produces a plate having a high frequencythickness coeilicient, and the plus 30 degree angle produces a crystalhaving a low frequency-thickness coeiiicient.

There are two kinds of quartz, namely, righthanded and left-handed. Inthe case of righthanded quartz, the convention is adopted that apositive angle is a clockwise rotation of the principal axis (opticaxis) when the electrically positive face as determined by a squeeze, isup. For left-handed quartz, a positive angle is a counterclockwiserotation of the principal axis when the electrically positive face isup.

Angles other than those given in the foregoing paragraph may be used,however, if the angle o departs from the angles given by more than plusor minus 10 degrees, the operation of the crystal plate as an harmonicoscillator becomes unsatisfactory, apparently due to the lower activityof the crystal plate as an oscillator and also because of the highercoupling coeilicient in the crystal to other vibrations.

The orientation of the crystal plate 2 with respect to thecrystallographic axes x, y and z is illustrated in Fig. 2, wherein thesubstantially parallel relation of the sides 3 and l to the a: axis, andan angle o between these sides and the z axis is shown.

One of the possible circuit arrangements illustrated in Fig. 3 lshowsthe crystal plate 2 connected to control the frequency of an electricdischarge device oscillation generator. The contact members 6 associatedwith the crystal plate 2 are of brass, bronze, Icopper, and likematerials and are connected across the grid resistor 'I which isconnected to the grid electrode 8 and cathode 9 of the tube 5. The anodeI is connected to the oscillatory circuit I I which includes aninductance unit I2 and a variable condenser I3. A source of anodecurrent supply I4, shunted by the by-pass condenser I5, is connected tothe voscillatory circuit II and the cathode 9.

The operation of the circuit illustrated in Fig. 3 is as follows: Thecondenser I3 is adjusted to tune the oscillatory circuit I I to anharmonic frequency of the crystal plate 2, corresponding to thefrequency of electrical oscillations that it is desired to produce. Thecrystal plate 2 impresses electric charges in the form of oscillationson the grid 8 of the tube 5 corresponding to the frequency to which thecircuit II is tuned. These oscillations may be of a frequency muchhigher than the fundamental frequency of the crystal, as brought out inthe preceding paragraphs herein, and yet electrical oscillations ofultra-high frequencies, derived from the oscillation generator andimpressed upon the inductance I6, are of sufficient power and potentialto be themselves suitable for driving an amplifier.

Fig. 4 illustrates the crystal plate of my invention vibrating at itsfundamental frequency in shear or transverse vibration. The distributionof the positive and negative electrical charges on the crystal plate, isshown for a particular instant. 'Ihis same crystal plate, vibrating atthe third harmonic, is illustrated in Fig. 4b. The frequency of theoscillations derived from the crystal, vibrating as illustrated in Fig.4b is three times the frequency` derived from the crystal plate,vibrating as illustrated in Fig. 4a. The crystal in Fig. 4b may beconsidered as divided into three imaginary crystal plates a, b and c asdefined by the dotted lines. The -electrical charges on these imaginarycrystal plates are designated, for a given instant by the plus and minussigns and it is seen that the polarity of the imaginary plate b is thereverse of that of the plates a and c, making the polarity on thesurfaces of the crystal at a given instant, of opposite sign; acondition necessary for sustaining oscillations and a condition whichalways exists when operating the crystal at the odd harmonics.

By defining the angle 0 of the electrode faces of my crystal element orplate as substantially -19 degrees or substantially +30 degrees withrespect to the a axis of the crystalline'body, in the claims forming apart hereof, it is intended that this angle 9 may vary within limits setforth in preceding parts of this specification.

It willbe observed that; have described an embodiment of my invention indetail however, I do not desire to limit this invention to the exactdetails set forth except insofar as those details are defined by thefollowing claims.

What I claim and desire to secure by Letters Patent of the United Statesis as follows:

l. A piezo-electric crystal cut from a crystalline body and`adapted foroperation in a shear mode at an odd harmonic, said odd harmonic being ahigh or ultra high frequency, said crystal being so cut that itselectrode faces are substantially parallel to an :c axis of thecrystalline body and make an angle of substantially -19 degrees with thez axis of the crystalline body.

2. A method of operating a crystal at an odd harmonic in a shear modewhich comprises so cutting the crystal that its electrode faces areparallel to the :v axis and make an angle of substantially -19 degreeswith the z axis and applying a eld of a frequency corresponding to thedesired shear mode harmonic.

3. A piezo-electric crystal cut from a crystal-v line body adapted foroperation in a shear mode at an odd harmonic said odd harmonic being ahigh or ultra high frequency, said crystal being so cut that itselectrode faces are substantially parallel to an x axis of thecrystalline body and make an angle of substantially -19 degrees with thez axis of the crystalline body, said angle being such as will produce a10W coupling coefficient in the crystal JOHN M. WOLFSKILL.

to other mode vibrations. 10

